Firstly, is there any reason you should not be on that tax code eg additional income from a rental property.
Secondly, doublecheck all your figures in case there is any error.
I was being charged double tax I initially thought was emergency tax so rang HMRC who said I had underpaid tax so owed them money and they had been taking it from my wages!
Your calculations with one job should be far simpler than mine (same place but three separate employers and weekly to monthly pay and sometimes different hours!).
I got every payslip and made a spreadsheet of all pay and deductions (make sure you include things like non-raxable pension contributions properly). I checked my figures against salary calculators showing the tax due on my correct tax code (backdated ones here -
https://www.payslipsp...alaryCalculator.aspx) and HMRC's own one with total figures.
After a number of headbanging phonecalls with HMRC I got them to send me a breakdown of the figures (took a while!) which confirmed that they had the wrong figure for the pay I'd received.
They tried to pin this on one of the agencies I was employed through, saying one of them must have got the figures wrong, so I double-checked the P45 figures (all correct) and got statements of earnings from both and sent them to HMRC to show THEY had got the figures wrong so their system was showing I had earned a lot more than I had and therefore underpayed tax!
It's taken a while (4 week turnaround I was told) but my tax code has been sorted and I just got a rebate!
Definitely worth checking if your yearly P60 figures or other figures (or payments made to them for your tax!) they have for your earnings and tax liability are correct - if you have all the figures to hand (what you paid and what you should have paid) it's easier to see what might have gone wrong where and who is at fault.
If you have a HR/payroll department or workplace accountant then they may be able to provide a statement of earnings.
Have you heard about this happening to anyone else that you work with?